US police are searching the home of suspected gunmen who attacked a conference on cartoons of the Prophet Muhammad in Dallas, officials say.
An FBI official said agents were collecting evidence at an apartment in Phoenix, Arizona.
One suspect was identified as Elton Simpson, who had been previously investigated on suspicion of terrorism offences, US media reported.
Two gunmen were shot dead after opening fire outside the contest on Sunday.
They drove to the Muhammad Art Exhibit in the Dallas suburb of Garland as the event was ending, shooting at and wounding a security officer before being killed by police.
Sunday evening's event was organised by the American Freedom Defense Initiative (AFDI), which is run by controversial blogger and activist Pamela Geller.
One of the keynote speakers was the Dutch politician Geert Wilders, an outspoken critic of Islam in Western societies.
The conference included a contest that offered a $10,000 (£6,600) prize for a cartoon of the Prophet Muhammad. Depictions of the Prophet Muhammad are offensive to many Muslims.
Officials believe that Simpson sent several Twitter messages before the Sunday's shooting, including one with the hashtag #texasattack part of which read: "May Allah accept us as mujahideen" [holy fighters]. The Twitter account was later suspended.
Simpson was reportedly convicted several years ago for lying to authorities about his plans to travel to Africa.
The bomb squad was called in to search the vehicle that the suspected gunmen arrived in. A vehicle was blown up as a precaution overnight, local TV station WFAA reported.
The suspects' bodies remained at the scene on Monday morning, surrounded by dozens of empty shell casings.
Security had been tight ahead of Sunday's conference and Garland's mayor acknowledged that there had been a lot of local concern about the event, though police said there had been no credible threats.
Geller said she was standing up for free speech, adding: "This terrible incident reflects the need for such conferences."
"We are continually abridging our freedoms so as not to offend savages," she said. She denied she was anti-Muslim, only "anti-jihad".
There were widespread protests in 2006 when the Danish newspaper Jyllands-Posten published cartoons satirising the Prophet Muhammad.
In January this year, 12 people were murdered by two Islamist gunmen at the French magazine Charlie Hebdo, which had published similar cartoons.
And a gathering of free speech activists in the Danish capital Copenhagen was targeted by a gunman in February, killing a film director.
Pamela Geller: America's controversial blogger
- A staunch critic of Islam since 2005, she rose to prominence in 2010 through her online opposition to Park 51, a planned Muslim community centre in Lower Manhattan close to the World Trade Center site
- Heads the American Freedom Defense Initiative (AFDI), which has also caused controversy by buying advertising space on buses in US cities, criticising Islam
- The 56-year-old describes herself online as a free-speech activist, but her critics denounce her as a "bigot"
- She insists the focus of her criticism is chiefly against radical Islam, but has been quoted as saying that "Islam is the most anti-semitic, genocidal ideology in the world"
- Speaking of her role in organising the Muhammad Art Exhibit in Garland, she said: "We draw Muhammad because we are free... We draw Muhammad because our unalienable rights are enshrined in the First Amendment."